In general, an optical scanning device installed in an image forming apparatus such as a copy machine includes a light source, a rotating polygon mirror that deflects light beam emitted from the light source unit and allows the deflected light beam to be scanned in a main scanning direction, an image forming lens that forms an image of the light beam deflected and scanned by the rotating polygon mirror on a surface to be scanned at a constant velocity, and a housing that receives devices such as the rotating polygon mirror and the image forming lens.
In this type of optical scanning device, the temperature of the image forming lens is changed due to frictional heat and the like at the time of rotation of the rotating polygon mirror, resulting in a change in a refractive index thereof. Therefore, there is a problem that a position in the main scanning direction of the scanning light having passed through the image forming lens is changed and thus image failure (image failure such as a color shift in the case of a color optical scanning device machine) occurs.
In this regard, for example, Patent Literature 1 discloses a technology in which the surface temperature of the image forming lens is detected by a temperature sensor and a writing start timing of image data is corrected on the basis of the detected temperature, so that a positional shift in the main scanning direction of the scanning light is corrected. In an optical scanning device disclosed in Patent Literature 1, the temperature sensor is provided at an upper side of the image forming lens.
As an arrangement configuration of a scanning optical system in the aforementioned optical scanning device, there has been known an opposed scanning type arrangement configuration in addition to a configuration in which the scanning optical system including the image forming lens is disposed only at one side of a polygon mirror as disclosed in Patent Literature 1. In the opposed scanning type arrangement configuration, the scanning optical system is disposed at the other side as well as the one side of the polygon mirror.